i have a 1996 bonneville SE and i replaced the stock hubcaps and p215/60/r15 tires with 2001 grand am gt wheels with p225/50/r16 tires.

i know for sure that the speedometer is too fast by 13 mph(when my speedometer says 30mph i am really only going 17mph).

i recently bought a quarter take of gas and set the trip odemeter, i was suprised to see that when i ran low on gas again the trip said i had gone 62 miles.(not driving conservitively at all). i am aware that the gas gauges on theese cars are not 100% accurate, but if my speedometer is too fast does that make my odometer put on 2 miles when i acually only when like 1 mile for example?

could i be racking up doulble miles?

yes, your car thinks you are going farther than you actually are....you are putting alot more miles on your car than are correct.

damn that'* not good, does anybody have any idea on the price of a speedometer calibration?

Something else is wrong. The outside diameter of your tires would have had to change by 57% to make the speedo be off that much. If the original tires had an outside diameter of 24 inches the new tires would only be 13.7 inches.

Edit - Your speedometer might be set for Kilometers

There'* more KM'* in a mile..

It sounds like you put larger tires on..not smaller. Therefore you'd be travelling further not..less.

Something is odd. YOu filled til the click and how much went in on the refill?

1.6 kms to be exact.

I wouldn't think your speedo should be off by THAT much.

I'm confused...if the tires were smaller, they'd make more revolutions quicker so wouldn't that mean he'd be traveling further according to the odometer? Wow it'* Friday i should stop thinking

If two trains leave the train station at the same time, heading in opposite directions and the first train is traveling 18mph faster than the second train and the second train has 142 miles farther to go than the first, how long after the first train arrives at its destination before the second train arrives?

Now to get back to topic:

Smaller tires than factory: less distance travled per the speed-o-meter
Larger tires than factory: more distance travled per the speed-o-meter

Thanks for clearing that up I got it after thinking further. Larger tire = Longer distance for wheel to travel.

I would recomend that a GPS be taken out and compared against the car and also checking the tier size per GM. That should give you an idea where your at

if the speedo is showing 30 kilometers your going about 18.641 mph.